You don't need to solve the Hunter Vault puzzle in Enshrouded to retrieve the NPC helper, but if you're a completionist like me, you'll want to unlock the door anyway. Once you retrieve the Hunter, you can place them at your camp where you can set up a drying rack, as well as access other handy items, such as a bag.
The Hunter Vault is found to the northeast of the Longkeep, on the other side of the Shroud-filled canyon. You can reach the far side easily enough via Braelyn Bridge if you have the grappling hook—which, coincidentally, you'll need inside the vault—otherwise, you can use your glider to get as far as you can before making the rest of the way on foot. Whichever way you choose to go, here's how to solve the Hunter Vault puzzle when you get there.
Enshrouded Hunter Vault puzzle: How to unlock the door
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There are a few enemies to deal with outside the Hunter Vault, but nothing too troublesome. Once you head inside through the main doors, navigate past blue electric bolts and head up the stairs between the two burning braziers.
From here, find a locked door to the right of the stairs and another locked door to your left, this one with a chest visible inside—take note of the three symbols above the door here too. There are three switches that you need to press to get inside, and one of them is pretty well hidden.
Here are the locations of the three switches:
The first switch is on the pillar to the right of the stairs. Shoot it with an arrow to unlock the door on the right.
The second switch is inside the door you just opened.
The third switch is directly above the main door to the vault—you can just make out the glow from the stairs.
To get to the third switch, stand close to one of the braziers and do a running jump in the direction of the door and deploy your glider briefly. There's a grapple point above you but you won't be in range until you're mid-glide so get ready to hit that grapple button—the E key in my case. You'll see two climbable surfaces to either side of the ledge above the door and you need to line up your jump so you swing in the direction of one of them and can grab it.
It may take a bit of practice to get the timing right but you'll get it. Once you climb onto the ledge, interact with the switch there and the door to the left of the stairs will open for you. Now you can loot the chest for an epic Bronze Sword.
If you're after the Hunter NPC, you can find them by using the grapple hook to cross the lava at the top of the stairs, then head up to the next level to find them inside the room at the top. You can also nab yourself a Forest Longbow here if you go up the stairs close to the door of the Hunter's room—there's a grapple point here too, and a linear path that takes you out onto the roof where you'll find another chest containing the bow.